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REPORT 


OF 


A  COMMITTEE 

OF  THE 

AMERICAN  ACADEMY  OF  ARTS  AND  SCIENCES 


ON 


VENTILATORS  AND  CHIMNEY-TOPS. 


I 

March,  1848. 


CAMBRIDGE  : 

METCALF  AND  COMPANY, 

PRINTERS  TO  THE  UNIVERSITY. 


1848. 


* 


V 


* 


) 

■  \ 


♦  •  x  -A  « •  jr'  • 


COMMITTEE, 

Prof.  BENJAMIN  PEIRCE, 

“  JOSEPH  LOVERING, 

“  EBEN  N.  HORSFORD, 
Dr.  MORRILL  WYMAN. 


% 


IWBGSTTYCENTcR 

UBHAHY 


R  B  r  0  R  T. 


Dr.  M.  Wyman,  from  the  Committee,  appointed  at  the  Oc¬ 
tober  meeting,  to  make  experiments  for  testing  the  value  of 
the  principal  kinds  of  ventilating  apparatus  now  in  use,  made 
a  report,  of  which  the  following  is  an  abstract. 

“  The  apparatus  used  in  most  of  the  following  experiments  consists, 
1st,  of  a  machine  for  producing  and  maintaining  a  constant  and  equable 
blast  of  air;  2d,  of  an  arrangement  for  measuring  the  velocity  of  the 
current  produced  by  this  blast. 

“  The  air  is  put  in  motion  by  means  of  a  revolving  fan  of  four  blades 
or  vanes,  each  21  inches  long  by  10  inches  wide,  placed  upon  the  ex¬ 
tremities  of  radii  13  inches  in  length.  These  blades  revolve  within  a 
cylindrical  case,  nearly  concentric  with  the  axis  of  the  blades,  to  which 
the  air  gains  admission  by  two  circular  openings  13  inches  in  diameter, 
one  in  either  end  of  the  case.  From  one  side  of  this  case,  the  air, 
put  in  motion  by  the  blades,  enters  a  trunk  3  feet  in  length,  and  at  its 
commencement  21  inches  wide  by  18  inches  deep,  which  is  gradually 
contracted  until,  at  its  farther  extremity,  its  cross  section  becomes  a 
square  of  100  inches  area.  To  the  mouth  of  this  trunk  another  is 
fitted,  also  10  inches  by  the  side  and  3  feet  in  length.  This  last  was 
added  to  avoid  any  interfering  or  unequal  currents  which  might  be 
produced  by  the  converging  sides  of  the  first.  Upon  the  axis  of  the 
blades  is  fixed  a  pinion  of  sixteen  leaves,  which  engages  a  wheel  of 
eighty  teeth,  driven  by  a  handle  ;  consequently  the  blades  revolve 
with  five  times  the  velocity  of  the  handle,  or  300  times  per  minute 
when  the  handle  makes  one  revolution  per  second.  This  is  the  ve¬ 
locity  always  used  in  the  following  experiments,  unless  otherwise 
stated. 

“  To  measure  the  velocity  of  the  blast,  a  toy  marble,  .62  inch  in 
diameter,  is  suspended  by  a  silken  thread,  to  which  it  is  fastened  by  a 
little  sealing-wax.  This  thread  is  3  feet  in  length,  and  the  point  of 


4  (30S)  PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 

suspension,  over  the  mouth  of  the  trunk,  is  such  that  the  marble  hangs 
as  nearly  as  possible  in  its  centre.  The  handle  is  made  to  revolve  ac¬ 
curately  once  a  second,  and  the  deflection  of  the  marble  from  the  point 
of  rest,  under  the  influence  of  the  blast  thus  produced,  observed.  The 
marble  is  then  protected  from  the  blast,  and  the  effect  of  the  blast  upon 
the  thread  alone  observed  and  deducted  from  the  first  result.  To  as¬ 
certain  the  value  of  this  deflection,  the  following  method  is  adopted. 
Into  a  large  cylindrical  vessel,  filled  with  water,  a  pipe,  an  inch  in  di¬ 
ameter  and  bent  into  the  form  of  an  inverted  syphon,  is  so  placed,  that, 
while  one  of  its  branches  rises  in  the  centre  of  the  vessel,  an  inch 
above  the  surface  of  the  water,  the  other  branch  rises  along  the  side 
of  the  vessel,  over  which  it  is  bent  nearly  horizontally.  Another  and 
similar  vessel  15.5  inches  in  diameter  at  the  top,  14  inches  at  the  bot¬ 
tom,  and  8.25  inches  in  depth,  is  inverted  upon  the  surface  of  the 
water  in  the  first.  By  pressing  down  this  second  vessel  the  contained 
air  is  made  to  issue  from  the  open  extremity  of  the  pipe  ;  and  as  the 
areas  of  the  vessel  and  pipe  are  both  known,  we  have  but  to  note 
the  time  required  to  empty  the  second  vessel  to  learn  the  velocity  of  the 

escaping  air.  The  marble  is  now  suspended  by  the  same  thread ;  the 

* 

point  of  suspension  being  so  situated  that  the  marble  falls  against  the 
mouth  of  the  pipe,  and  would,  if  allowed  to  move  freely,  hang  as  far 
within  it  as  the  marble,  deducting  the  effect  upon  the  thread,  was  de¬ 
flected  by  the  blast.  The  second  vessel  is  now  depressed  with  such 
velocity  that  the  marble  is  just  made  to  swing  clear  of  the  mouth  of  the 
pipe,  by  which  its  deflection  becomes  precisely  that  produced  by  the 
blast  which  is  to  be  measured. 

“In  the  case  under  consideration,  the  deflection  of  the  thread  and 
marble  together  was  2.5  inches  ;  that  dependent  upon  the  thread  alone, 
.95  inch.  The  time  occupied  in  depressing  the  vessel  until  it  rested 
upon  the  top  of  the  inverted  syphon,  in  several  successive  experiments, 
was  12.25  seconds.  The  contained  air  was  compressed  .25  inch  to 
produce  this  velocity,  and,  as  the  pipe  rose  1  inch  above  the  surface  of 
the  water,  1.25  inches  were  deducted  from  the  depth  of  the  vessel,  leav¬ 
ing  an  available  depth  of  7  inches.  The  mean  diameter,  that  at  the 
top  being  15.5  inches,  and  at  the  bottom  14  inches,  is  14.75  inches. 
As  the  areas  of  circles  are  to  each  other  as  the  squares  of  their  diam¬ 
eters,  we  have  these  areas  in  the  proportion  of  217.56  to  1.  This 
number  multiplied  by  the  depth  in  inches,  7,  gives  the  whole  expendi¬ 
ture  in  12.25  seconds,  the  time  required  to  empty  the  vessel ;  from  which 


OF  ARTS  AND  SCIENCES. 


(309)  5 


we  obtain  a  velocity  of  124.32  inches,  or  10.36  feet,  per  second, — 
7.06  miles  per  hour.  This,  therefore,  may  be  assumed  as  a  near  ap¬ 
proximation  to  the  velocity  of  the  blast,  when  not  otherwise  mentioned. 

“  The  velocity  of  the  induced  current  being  the  true  measure  of  the 
practical  value  of  different  forms  of  ventilating  apparatus,  it  becomes 
necessary  to  ascertain  this  value  as  accurately  as  possible.  The  in¬ 
convenience  attending  measurements  in  which  time  is  involved  as  one 
of  the  elements,  and  also,  probably,  the  difficulty  of  determining  the 
instant  when  a  current  has  passed  through  a  certain  space,  have  led  to 
the  adoption  of  other  means,  by  which  the  velocity  of  the  current  is 
not  directly  measured,  but  inferred.  The  mode  which  has  been  re¬ 
peatedly  adopted,  of  measuring  the  efficiency  of  a  ventilator  by  its 
power  of  sustaining  a  weighted  flap  or  valve,  or  a  head  of  water,  or 
by  some  other  statical  effect,  is  decidedly  objectionable.  Such  a  meas¬ 
ure  gives  the  correct  value  of  the  initial  force  or  tendency  to  establish 
a  current  in  a  chimney  in  which  there  is  no  actual  movement ;  but  it 
does  not  indicate  the  velocity  of  the  current  which  will  be  the  final 
result  of  the  action  of  the  ventilator,  nor  is  it  any  measure  of  this 
final  velocity  when  ventilators  of  different  construction  are  compared 
together.  Mechanics  and  engineers  are  familiar  with  the  difference 
between  the  statical  and  dynamical  effects  of  a  force.  They  are  aware 
that  the  former  may  be  greatly  increased  by  the  mechanical  powers, 
so  that,  through  the  medium  of  a  pulley  or  a  lever,  a  single  pound  may 
be  made  to  sustain  and  raise  a  hundred  times  its  own  weight.  But  the 
dynamical  effect  is  not  correspondingly  increased,  for  in  order  to  raise 
one  hundred  pounds  through  the  height  of  a  foot,  the  one  pound  must 
in  all  cases  fall  one  hundred  feet ;  so  that  the  loss  of  height  precisely 
balances  the  gain  in  weight.  In  the  same  way,  the  dynamical  effect 
of  different  springs  is  not  to  be  measured  by  their  strength  alone  ;  it  is 
not  simply  dependent  upon  the  amount  of  weight  which  they  will  sus¬ 
tain,  but  equally  upon  their  length,  or  rather  upon  the  distance  through 
which  they  move  in  restoring  themselves  to  equilibrium.  The  archer’s 
bow  is  a  good  instance  of  this  assertion,  which  any  one  can  try  for 
himself,  and  he  will  find,  that,  with  a  given  exertion  of  strength,  he  is 
able  to  throw  the  arrow  farthest  and  highest  with  that  long  bow  of 
which  he  can  draw  the  string  to  his  full  arm’s  length,  and  not  with  the 
strong  bow  which  he  can  hardly  move.  But  an  example  more  nearly 
allied  to  the  case  under  consideration  is  derived  from  the  air-pump,  in 
which  the  dynamical  value  of  any  amount  of  exhaustion  is  equal  to 


6  (310)  PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 

the  power  required  to  produce  it,  and  is,  therefore,  proportioned  to  the 
magnitude  of  the  receiver  when  other  circumstances  are  the  same ; 
whereas  its  statical  power  or  its  power  to  sustain  a  head  of  water  is 
wholly  independent  of  the  magnitude  of  the  receiver,  and  proportioned 
solely  to  the  tension  of  the  air  within  it.  In  all  these  cases,  there  is  a 
striking  difference  between  the  operations  of  using  the  statical  and 
dynamical  effects,  which  deserves  the  most  careful  consideration,  be¬ 
cause  it  is  essential  and  characteristic.  The  statical  effect  may  be 
used  for  any  length  of  time  without  being  impaired,  and  the  reason  is 
obvious  ;  it  manifests  itself  in  a  state  of  rest,  when  there  is  no  change 
of  condition.  The  dynamical,  on  the  contrary,  can  be  used  once  and 
but  once.  The  one  pound  can  balance  the  hundred  pounds  as  long  as 
the  materials  of  the  pulley  and  lever  will  endure  ;  a  compressed  spring 
may  sustain  its  weight,  or  the  expanded  air  its  head  of  water,  as  long 
as  we  choose,  without  any  diminution  of  effect.  But  when  work  is  to 
be  done,  a  change  to  be  effected,  a  weight  to  be  raised,  a  velocity  to 
be  produced,  the  result  can  only  be  obtained  by  a  corresponding  change 
in  the  opposite  direction,  an  undoing  of  work,  a  falling  of  a  weight,  a 
consumption  of  power  once  and  for  ever.  In  the  present  case,  in  which 
the  object  is  to  obstruct  or  divert  the  motion  of  the  wind  in  such  a  way 
that  part  of  its  velocity  may  be  communicated  to  the  air  in  the  chimney, 
and  thus  produce  a  current,  the  amount  of  this  communication  and  trans¬ 
fer  of  velocity  cannot  be  measured  when  it  does  not  take  place,  —  when, 
on  the  contrary,  the  mouth  of  the  chimney  is  entirely  stopped  up,  so  that 
it  is  impossible  to  produce  any  current  within  it.  It  would  be  just  as 
proper  to  weigh  a  water-wheel  by  the  weight  which  will  just  reduce  it 
to  a  state  of  rest,  instead  of  that  smaller  weight  which  reduces  it  to  its 
usual  working  velocity,  and  which  is  universally  adopted  by  experi¬ 
enced  engineers  as  the  correct  measure  of  the  power  of  the  wheel. 
It  should  also  be  borne  in  mind,  that  there  are  resistances  offered  to 
air  in  motion  by  the  tube  through  which  it  passes.  These  resistances 
are  not  constant ;  they  increase  as  the  perimeter  and  length  of  the  tube 
directly,  and  also  as  the  square  of  the  velocity  ;  these,  it  is  obvious, 
cannot  be  measured  where  they  do  not  exist. 

“  The  plan,  therefore,  which  has  been  adopted  in  these  experi¬ 
ments,  is  to  measure  directly  the  velocity  of  the  current  produced,  and 
it  will  not  be  surprising,  after  what  has  preceded,  if  some  striking  dif¬ 
ferences  should  be  observed  between  the  results  thus  obtained  and 
those  derived  from  any  statical  measure. 


OF  ARTS  AND  SCIENCES. 


(311)  7 


“  To  measure  the  current,  a  leaden  pipe  (the  material  most  readily 
at  hand),  1.25  inches  in  diameter  and  53  feet  in  length,  is  placed  near 
and  a  feW  inches  below  the  mouth  of  the  blowing-machine.  This 
pipe  is  coiled,  as  it  leaves  the  manufactory,  into  a  circle  of  about  2.5 
feet  in  diameter,  of  which  it  makes  eight  turns.  In  the  mouth  of  the 
trunk,  before  described  as  attached  to  the  blowing-machine,  is  a  tube 
of  tinned  iron,  of  the  same  diameter  as  the  pipe,  and  bent  at  a  right 
angle  ;  the  upright  branch,  about  six  inches  long,  reaching  to  the  mid¬ 
dle  of  the  mouth,  while  the  horizontal  portion,  about  five  inches  in 
length,  reaches  within  2.5  inches  of  the  end  of  the  leaden  pipe.  Each 
ventilator,  when  examined  and  tested,  is  placed  upon  the  upright  por¬ 
tion  of  this  tube.  For  this  purpose  the  ventilator  has  through  it,  or 
attached  to  its  side,  a  corresponding  tube  of  the  same  diameter.  The 
connection  between  these  two  tubes  is  completed  by  a  glass  tube  4 
inches  long  and  2  inches  in  diameter,  and  the  fitting  made  close  by 
means  of  cotton-wool  fastened  loosely  around  the  extremities  of  the 
two  metallic  pipes.  In  this  compound  pipe  the  current  is  induced,  and 
its  velocity  noted.  To  effect  this  last  object,  advantage  is  taken  of  the 
well-known  action  of  iodine  upon  starch.*  Iodide  of  potassium  is  dis¬ 
solved  in  a  strong  solution  of  starch  in  hot  water,  in  the  proportion  of 
three  grains  or  more  of  the  iodide  to  an  ounce  of  the  solution.  A 
piece  of  paper  wetted,  or  rather  smeared,  with  the  prepared  starch  is 
suspended  within  the  glass  tube,  which  can  be  readily  removed  for  this 
purpose,  by  means  of  a  wire  hook  attached  to  the  metallic  pipe.  A 
current  is  now  induced  by  the  action  of  the  blast  upon  the  ventilator, 
and  chlorine  gas  allowed  to  enter  the  opposite  end  of  the  pipe,  which 
is  kept  carefully  removed  from  the  influence  of  the  blast.  The  chlo¬ 
rine  is  carried  along  with  the  current  until  it  reaches  the  starched 
paper,  which  it  instantly  dyes  a  deep  blue ;  the  chlorine,  by  its  superior 
affinity  for  the  potassium,  seizing  upon  it,  and  leaving  the  iodine  free 
to  act  upon  the  starch. 

“  Chlorine  is  conveniently  obtained  for  this  purpose  from  Labar- 
raque’s  solution  of  chloride  of  soda,  and  its  liberation  quickened,  if  need 
be,  by  adding  a  few  drops  of  sulphuric  acid.  When  the  vial  contain¬ 
ing  the  chlorine  is  closed  by  the  finger,  and  held  a  few  seconds  in  the 

*  The  action  of  hydrosulphuric  acid  upon  moist  carbonate  of  the  oxide  of  lead 
was  first  suggested  for  this  purpose,  but  the  chlorine  and  iodide  were  judged 
most  convenient. 


8  (312)  PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 

hand,  its  warmth  expels  the  gas  more  freely,  and  when  the  finger  is 
removed  it  escapes  in  a  jet,  which  makes  the  experiment  more  de¬ 
cisive. 

“  In  making  the  following  experiments  three  persons  were  usually 
employed ;  one  to  keep  up  a  uniform  blast,  counting  the  revolutions 
of  the  handle  by  a  watch ;  a  second  to  throw  the  chlorine  into  the 
pipe,  and  also  to  observe  and  declare  the  moment  when  the  blue  color 
appears  upon  the  starched  paper  ;  the  third  to  note  upon  a  watch  the 
interval  between  these  two  events. 

“  Results  of  Experiments. 

“  1.  Air  in  motion  communicates  motion  to  those  portions  of  air  at 
rest  in  its  immediate  vicinity.  To  this  phenomenon  Venturi,  who 
discovered  and  explained  it,  has  given  the  name  of  the  lateral  com¬ 
munication  of  motion  in  fluids. 

“2.  A  jet  of  air  falling  upon  any  surface  is  never  reflected,  but 
spreads  itself  out,  and  forms  a  thin  layer  in  immediate  contact  with 
that  surface.  It  may  be  admitted  as  a  principle,  that  fluids  do  not, 
under  any  velocity  or  any  angle  of  incidence,  possess  the  property  of 
reflection,  like  solids,  and  it  is,  doubtless,  owing  to  the  absence  of  this 
property  that  they  adhere  to  bodies  against  which  they  strike.  In  vir¬ 
tue  of  this  adhesion,  a  jet  of  fluid  striking  a  sphere  perpendicularly  to 
its  surface  spreads  itself  uniformly  over  both  the  superior  and  inferior 
hemispheres  ;  a  similar  jet  striking  a  horizontal  cylinder  perpendicu¬ 
larly  to  its  surface  completely  surrounds  it,  and  does  not  leave  it  until 
the  two  parts  of  the  jet  meet  on  its  inferior  border  and  form  one  com¬ 
mon  sheet.  (Savart,  Annales  de  Chimie  et  de  Physique ,  Tom.  LIV.) 

“  When  a  jet  of  water  strikes  a  truncated  cone  perpendicularly  to  its 
axis,  and  just  above  its  lower  base,  it  spreads  out,  covering  more  than 
half  its  surface,  and,  rising  upward,  leaves  its  upper  base  in  a  continu¬ 
ous  sheet,  vertically  in  a  plane  nearly  coinciding  in  direction  with  that 
of  the  sides  of  the  cone,  and  horizontally  nearly  in  the  direction  of 
tangents  to  the  surface  of  the  cone,  while  a  small  portion  only  of  the 
fluid  forms  two  small  streams,  which  drop  down  from  those  two  points 
of  the  lower  base  of  the  cone  which  are  at  right  angles  with  the  orig¬ 
inal  direction  of  the  jet. 

“  When  a  jet  meets  a  circular  plane  at  its  centre  and  perpendicular¬ 
ly,  it  forms  a  thin  continuous  sheet  over  the  whole  surface.  Both  the 
direction  and  continuity  of  this  sheet  are  preserved  far  beyond  the 


OF  ARTS  AND  SCIENCES. 


(313)  9 


borders  of  the  circular  plane,  where  its  edge  is  thin,  but  it  follows 
more  or  less  the  direction  of  the  curve  of  the  edge,  if  it  is  thick  and 
rounded.*  (Savart,  Ann.  de  Chim.  et  de  Physique,  Tom  LIV.  p.  119.) 

“  3.  When  a  jet  of  air  impinges  upon  a  surface  of  limited  extent,  the 
atmospheric  pressure  upon  the  opposite  side  of  the  surface,  in  conse¬ 
quence  of  the  lateral  communication  of  motion,  is  diminished,  and  a 
current  will  be  established  through  a  tube,  one  of  the  extremities  of 
which  is  placed  in  the  point  of  diminished  pressure,  and  the  other  be¬ 
yond  the  borders  of  the  surface.  This  is  the  important  principle  upon 
which  the  efficiency  of  ventilators  and  chimney-tops  depends  ;  it  is 
also  important  in  its  bearing  on  the  position  of  the  mouths  of  air-trunks 
for  hot-air  furnaces ;  if  the  mouth  be  placed  in  a  point  of  diminished 
pressure,  on  the  leeward  side  of  a  building,  air  may  pass  outward, 
especially  from  apartments  on  the  windward  side  of  the  house. 

“  4.  When  a  current  strikes  the  extremity  of  a  tube  perpendicularly 
to  its  axis,  motion  is  produced  through  the  tube  towards  the  current ; 
and  when  a  current  already  exists  in  the  tube,  if  its  velocity  is  less 
than  that  of  the  impinging  current,  that  velocity  will  be  increased. 

“  When  two  currents  of  air  of  different  velocities  are  moving  in  pre¬ 
cisely  the  same  direction,  the  influence  of  the  more  rapid  current  in 
accelerating  that  which  is  less  rapid  is  not  so  great  as  when  the  angle 
of  meeting  is  between  20°  and  40°.  When  two  opposite  currents  of 
equal  diameter  and  velocity  meet,  they  form  a  circular  sheet,  pei'pen- 
dicular  to  the  axis  of  the  veins,  and  the  resulting  phenomena  resem¬ 
ble  those  arising  when  a  current  strikes  a  circular  plane.  If  the  ve- 

*  A  simple  demonstration  of  these  propositions  may  be  obtained  by  means  of  a 
card  and  candle.  If  a  blast  from  the  mouth  be  directed  obliquely  against  a  card, 
the  flame  of  a  lighted  candle  will  be  drawn  towards  the  card,  on  whatever  side 
of  it  the  candle  is  held.  Increasing  or  diminishing  the  velocity  of  the  blast  does 
not  change  the  direction  assumed  by  the  flame,  but  only  the  velocity  with  which 
it  is  drawn  towards  the  card. 

If  the  blast  be  directed  perpendicularly  upon  the  centre  of  the  card,  the  flame, 
when  passed  around  the  edge  of  the  card,  will  be  driven  outward  at  all  points; 
and  if  the  candle  be  held  near  the  blast,  and  at  a  little  distance  from  the  plane 
surface,  the  flame  will,  in  virtue  of  the  lateral  communication  of  motion,  be  drawn 
towards  the  surface,  and  yet  by  the  current  of  air  close  to  and  parallel  with  the 
card  it  will  be  prevented  from  reaching  it.  A  strong  flame  may  thus  be  made  to 
play,  apparently  with  great  force,  upon  the  hand,  and  yet  not  burn  it.  An  illus¬ 
tration  of  this  principle  may  often  be  observed  in  the  narrow  pathway,  so  con¬ 
venient  for  foot-passengers,  found  after  a  snow-storm,  on  the  windward  side  of  a 
high  and  close  fence. 


2 


10  (314)  PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 

locities  of  the  currents  are  unequal,  the  greater  velocity  diminishes  the 
less,  destroys  it,  or  inverts  it,  according  to  the  excess  of  velocity.  The 
knowledge  of  this  fact  leads  at  once  to  the  interposition  of  a  plate,  to 
prevent  loss  of  velocity  in  interfering  currents. 

“5.  A  thin  plate  placed  upon  the  extremity  of  a  tube,  at  the  proper 
angle,  causes  the  impinging  current  to  assume  a  certain  direction,  and 
to  produce  a  certain  velocity  in  the  tube  ;  a  similar  plate  parallel  to 
and  above  this  plate  does  not  increase  that  velocity. 

“  A  cone  placed  upon  the  extremity  of  a  tube  produces  similar 
changes  of  direction  in  the  impinging  current,  and  similar  movements 
in  the  tube,  but  another  cone  above  the  first  does  not  increase  the 
velocity  of  those  movements. 

“  6.  Beyond  certain  narrow  limits,  the  velocity  produced  in  a  tube 
by  the  action  of  a  current  on  its  conical  extremity  is  not  increased  by 
increasing  the  height  or  diameter  of  that  cone.  The  full  effect  of  a 
cone. may  be  obtained  when  its  lower  base  is  not  larger  than  one  half, 
nor  less  than  one  third,  the  diameter  of  the  flue  on  which  it  is  placed. 

“  7.  If  a  flat  truncated  cone  be  fitted  to  the  extremity  of  a  tube, 
and  exposed  to  the  impinging  current,  a  velocity  may  be  produced  in 
the  tube  of  1.71  feet  per  second  ;  if  a  similar  but  much  smaller  hollow 
truncated  cone  be  inverted  and  closely  secured  to  the  mouth  of  the 
first,  the  velocity  in  the  same  tube  may  by  this  means  be  increased  to 
2.21  feet  per  second.  The  same  increase  of  velocity  will  be  produced 
if  the  internal  cylindrical  bore  of  the  first  cone  be  made  conical,  with 
its  larger  base  upward.  By  the  addition  of  this  secondary  cone,  or  by 
the  modification  of  the  interior  of  the  first  cone,  the  velocity  of  the 
current  is  increased  over  that  produced  by  the  simple  cone  nearly  in 
the  ratio  of  10  to  13,  and  as  the  effect  is  as  the  square  of  the  velocity, 
its  efficiency  is  increased  nearly  in  the  ratio  of  10  to  17.  This  is 
the  best  form  of  the  simple  fixed  cone,  and  the  most  efficient  fixed, 
ventilator ,  which  has  been  examined  by  the  Committee.  Venturi  has 
shown,  that,  when  a  conical  tube  is  applied  to  a  cylindrical  pipe,  the 
larger  base  of  this  conical  tube  being  1.8  the  diameter  of  the  pipe, 
and  its  height  9  times  the  diameter  of  this  same  pipe,  the  expenditure 
will,  with  water,  be  greater  for  the  cone  than  for  the  cylindrical  pipe, 
in  the  proportion  of  24  to  12.1. 

“  8.  A  hollow  truncated  cone,  with  its  larger  base  closed  by  a  fiat 
plate,  inverted  and  placed  above  a  cone  similar  to  that  last  described, 
will  increase  the  velocity  of  the  current  in  the  pipe  upon  which  it  is 


OF  ARTS  AND  SCIENCES. 


(315)  11 


placed  over  that  produced  by  a  simple  cone  nearly  in  the  ratio  of  10 
to  13.  This  is  one  of  the  most  efficient  fixed  ventilators  with  a  cap 
which  have  been  examined  by  the  Committee.  The  form  described 
in  the  preceding  paragraph,  with  Cisalpin’s  plate  placed  at  a  certain 
height  above  it,  is  to  be  ranked  in  efficiency  with  that  last  described. 

“9.  The  velocity  of  the  current  produced  in  a  pipe,  the  mouth  of 
which  is  presented  fairly  to  the  blast,  is  nearly  constant,  whether  the 
mouth  be  cylindrical,  conical,  with  its  larger  base  towards  the  blast, 
or  the  reverse.  The  diminished  area  exposed  to  the  blast,  ip  the  latter 
case,  is  counterbalanced  by  the  increased  velocity  consequent  upon 
diminished  atmospheric  pressure  within  the  cone. 

“  10.  A  difference  of  temperature  between  the  impinging  blast  and 
the  produced  current  does  not,  within  the  limits  observed,  influence 
the  velocity  of  the  latter. 

“  Experiments. 


“  In  the  experiments,  each  ventilator,  when  examined,  is  placed  upon 
a  perpendicular  fixed  tube  of  tinned  iron,  in  the  centre  of  the  mouth 
of  the  trunk  of  the  blowing  machine.  This  and  all  other  tubes,  when 
not  otherwise  mentioned,  are  1.25  inches  in  diameter.  The  velocity 
of  the  blast  is  10.36  feet  per  second,  or,  as  indicated  by  the  revolutions 
of  the  handle  of  the  blowing-machine,  one  revolution  per  second. 
The  time  required  for  the  chlorine  to  act  upon  the  starch,  from  the 
moment  it  is  introduced  into  the  pipe,  is  given  in  seconds  ;  the  velocity 
of  the  current  is  given  in  feet  and  decimals.  The  direction  of  the 
blast  is  indicated  by  the  >. 


/&7ZZ7Z7  ^ 

Fig.  1. 


“  Experiment  1. 
fixed  tube, 


Perpendicular 


Time  in 
Seconds. 


73.2 


Velocity  per 
Second. 

Feet. 

0.728 


Fig.  2. 


“  Exp.  2.  Straight  tube,  cut  off 


obliquely  at  an  angle  of  45c 
turned  from  the  blast, 


opening 


40.0 


1.325 


“  Exp.  3.  Elbow  ;  horizontal  por¬ 
tion  one  inch  long,  opening  turned 
from  the  blast,  ....  72.0 


Fig.  3. 


0.736 


12  (316)  PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 


“  Exp.  4.  Elbow  ;  horizontal  portion  4  inches  long, 

Seconds. 

Second. 

Feet. 

opening  turned  from  the  blast,  .... 

“  Exp.  5.  Same  ;  horizontal  portion  making,  with 

70.0 

0.757 

the  direction  of  the  blast,  an  angle  of  30°, 

46.0 

1.152 

“  Same ;  angle 

of  direction  45°, 

41.0 

1.290 

“  Same ;  “ 

“  60°, 

43.0 

1.233 

“  Same  ;  “ 

Fig.  4. 

“  90°, 

“  Exp.  6.  Elbow  turned  from 

64.0 

0.828 

1V//A 


the  blast,  and  having  around  its 
opening  a  plane  surface  1.5 
inches  wide,  .... 


31.0  1.71 


“  Exp.  7.  A  perpendicular 
plate  2  inches  wide  and  1.75  inch¬ 
es  in  height,  fastened  to  that  side 
of  the  fixed  tube  next  the  blast,  . 
“  Same  plate  attached  to  the 
fixed  tube,  but  with  its  edges  in  the  same  direction 
with  the  blast,  ....... 

“  Same  plate  on  the  side  of  the  fixed  tube,  opposite 
the  blast,  .....  no  effect  in 


Fig.  5. 

> 

\ 

i 

i 

33.0 

48.0 

180.0 


1.61 

1.05 


“  Exp.  8.  A  square  plate,  2  inches  by  the  side,  on 
the  top  of  the  fixed  tube  on  the  side  next  the  blast,  . 

“  Same  plate  making  with  horizon  an  angle  of  80°, 
“  “  “  75°, 

«  «  “  70°, 

“  “  “  67°, 

“  “  “  45°, 

u  u  u  22° 

“  Exp.  9.  Square  plate,  2  inches  by  the  side,  with 
vertical  edges  .5  inch  wide,  turned  from  the  blast,  and 
making  an  angle  of  45°  with  its  direction  ;  the  whole 
plate  making  an  angle  of  75°  with  the  horizon, 

“  Same  plate,  making  same  angle  with  the  horizon, 
but  with  its  edges  turned  in  the  opposite  direction; 
that  is,  towards  the  blast,  .  .  .  .  . 


31.5 

28.2 

27.3 

29.0 

28.7 

39.0 

65.0 


31.0 


24.6 


1.63 

1.87 

1.94 

1.83 

1.85 

1.36 

0.791 


1.71 


2.15 


“  Exp.  10.  A  plate  1.25  inches  wide  at  the  base,  2 


OF  ARTS  AND  SCIENCES. 


(317)  13 


Time  in  Velocity  per 
Seconds.  Second. 

inches  wide  at  top,  and  2  inches  high,  with  its  edges 

turned  towards  the  blast,  as  in  the  last  experiment,  Feet. 

gave  very  nearly  the  same  results,  ....  24.7  2.14 


“  Exp.  11.  A  plate  2  inches  wide  at  the  base,  1.25 
wide  at  the  top,  and  1.5  inches  high ;  angles  of  sides 
with  base  equal  to  inclination  of  the  plate  with  the 
horizon,  76°  ;  placed  on  the  top  of  the  fixed  tube,  on 
the  side  next  the  blast,  its  base  being  raised  .37  inch 
above  the  mouth  of  the  fixed  tube,  ....  29.5  1.80 

“  A  similar  plate  added  to  the  opposite  side  of  the 
tube,  .........  28.5  1.86 

“  Similar  plates  on  three  sides ;  open  side  from  the 

blast, . 33.5  1.58 

“  Similar  plates  on  three  sides ;  open  side  at  right 
angle  with  direction  of  the  blast,  ....  32.2  1.65 

“  Similar  plates  on  four  sides,  ....  35.4  1.494 


“  Exp.  12.  Pyramid  formed  by  the  four  plates,  as 
last  arranged,  with  its  base  so  fitted  to  the  top  of  the 
fixed  tube  that  no  air  could  enter  by  its  side,  .  .  35.5  1 .49 

“  Exp.  13.  Two  similar  plates,  those  used  in  the 
last  experiments,  one  arranged  as  in  Exp.  10,  and  the 
other  similarly  placed,  but  raised  .37  inch  above  the 
first,  . . 29.0  1.83 


“  The  influence  of  the  inclined  plate,  used  in  several  of  the  preceding 
experiments,  would  at  once  suggest  the  application  of  a  figure  of  revo- 
olution,  which  would  have  a  similar  effect  upon  the  blast,  that  is, 
would  direct  it  upward,  and  thus  assist  the  escape  of  the  current  from 
the  tube.  A  cone  is  evidently  one  form  which  would  have  this  effect. 
Indeed,  the  conical  chimney-top  has  been  long  in  use,  and  its  principle 
often  reproduced  under  slight  modifications  of  form. 

“  The  cone  was  proposed  as  a  proper  form  for  the  chimney-top,  and 
an  account  of  its  application  published,  more  than  seventy  years  ago, 
by  Count  Cisalpin,  in  a  memoir  entitled  Description  d'une  Cheminee 
et  ittuve  de  Nouvelle  Invention.  The  plan  contrived  by  Cisalpin  con¬ 
sisted  of  truncated  cones  of  plate  or  sheet  iron,  of  different  sizes. 
‘  When  this  apparatus  is  to  be  used,’  says  he,  ‘  fit  to  your  chimney 
your  first  size ;  it  is  of  no  consequence  whether  the  chimney  be  round 


14  (318)  PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 


Fig.  6. 


or  square,  provided  it  have  no  holes  in  its  sides,  and  is  open  only  at 
the  top  ;  if  this  put  a  stop  to  the  smoking,  your  object  is  probably  ac¬ 
complished,  the  equilibrium  between  the  wind  and  smoke  is  destroyed 
(nevertheless  assure  yourself  of  this  by  many  experiments,  made  at 
different  times),  and  then  you  have  nothing  further  to 
do  than  to  attach  to  three  sides  of  the  cone  three 
rods  of  iron,  four,  five,  or  six  inches  long,  on  which 
place  horizontally  a  round  plate,  having  a  diameter  a 
little  larger  than  that  of  the  cone,  to  prevent  the 
rain  from  entering  the  chimney.’  The  adjoining 
figure  is  an  elevation  from  the  perspective  view 
given  in  the  memoir. 

“  In  1788,  De  Lyle  de  Saint-Martin,  a  lieutenant  in  the  French 
navy,  again  called  attention  to  this  form  of  chimney-top,  in  a  memoir, 
giving  a  full  description,  with  drawings,  of  its  construction,  and  the 
results  of  his  experiments.  The  cap  surmounting  the  cone,  instead  of 
Fig.  7.  being  flat  as  in  Cisalpin’s,  was  also  a  trun¬ 

cated  cone,  but  differing  in  its  proportions 
from  that  forming  the  chimney-top.  This 
arrangement,  which  is  here  figured  from 
Saint  Martin’s  memoir,  was  examined  and 
approved  by  the  French  Academy  of  Sciences, 
and  published  in  its  Transactions. 

“  Mr.  Tredgold,  in  his  treatise  on  Warming  and  Ventilating  Build¬ 
ings,  published  in  1824,  and  still  a  standard  work,  refers  to  the  conical 
top  as  one  which  may  often  be  employed  with  advantage, 
when  formed  in  the  manner  described  in  fig.  8 ;  and  re¬ 
marks, —  ‘  The  upper  cap  prevents  down  blasts  of  air,  but 
in  a  steady  horizontal  wind  the  lower  cone  alone  would 
be  sufficient.’  Its  mode  of  action  is  described  and  il¬ 
lustrated  by  figures,  from  one  of  which  the  annexed  cut 
is  copied.  For  its  origin  Mr.  Tredgold  refers  to  the  me¬ 
moir  of  De  Lyle  de  Saint-Martin.  It  will  be  noticed 
that  the  conical  cap  has,  in  the  last  figure,  assumed  the 
spherical  form. 

“  The  annexed  cut  shows  the  same  truncated  cone, 
which  has,  during  the  past  year,  been  introduced  as  quite 
a  novelty,  the  inventor  having  gone  back  to  first  princi¬ 
ples,  and  again  mounted  the  flat  top. 


Fig.  8. 


Fig.  9. 


0 

'Mfk 

in 

OF  ARTS  AND  SCIENCES. 


(319)  15 


“  It  is  quite  probable,  that  the  conical  and  pyramidal  earthen  and 
brick  chimney-tops  now  and  for  many  years  so  generally  used  are 
modifications  of  those  introduced  or  recommended  by  Cisalpin,  Saint- 
Martin,  and  Tredgold. 

Time  in.  Velocity  per 
Seconds.  Second. 

“Exp.  14.  A  truncated  cone,  diameter  of  upper 
surface  1.25  inches;  diameter  of  lower  surface  4.3 
inches;  height  1.3  inches  ;  lower  surface  upon  fixed  Feet. 

tube;  upper  surface  in  centre  of  trunk,  .  .  .  31.0  1.71 

“  Exp.  15.  Same  cone  divided  into  three  cones  of 
equal  height  by  planes  parallel  to  the  two  surfaces  ; 
two  smaller  cones,  ......  31.0  1.71 

“  Smallest  cone,  ......  31.5  1.6S 


“  Exp.  16.  Truncated  cone,  diameter  of  lower 
surface  2.1  inches  ;  height  .35  inch  ;  diameter  of  flue 
and  upper  surface,  as  usual,  1.25  inches,  .  .  31.0 

“  Inclination  of  sides  to  base,  in  these  last  cones, 
the  same ;  40°. 


Fig.  10. 


“  Exp.  17.  Cone  ;  angle  of  side 
with  base,  at  bottom  47°,  at  top 
55°,  side  concave  ;  diameter  of 
base,  3.7  inches  ;  height,  1.4 
inches,  ..... 

“  Exp.  18.  Cone  ;  angle  of  side 
with  base,  at  bottom  44°,  at  top 
64°,  side  concave;  base  4  inches 
in  diameter;  height  1.9  inches, 


“  Exp.  19.  Cone,  with  its  cap,  made  according  to 
the  proportions  laid  down  by  Saint-Martin  (see  fig.  7), 


35.4 


37.6 


34.0 


“  Exp.  20.*  Cone  and  plate  ;  inclination  of  sides  to 
base  45° ;  diameter  of  base  2.9  inches  ;  height  .83 
inch  (see  fig.  9),  ....... 


1.71 


1.49 


1.41 

1.56 


1.58 


*  Dimensions  of  cone  and  plate,  from  which  this  model  was  made,  as  fol¬ 
low  ; _ diameter  of  flue  18  inches  ;  base  of  cone  3ft.  6in. ;  height  of  cone  12in. ; 

diameter  of  plate  3ft.  6in. ;  height  of  plate  above  top  of  cone  9in.  ;  thickness  of 
plate  l^in. 


16  (320)  PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 

Time  in 
Seconds. 

“ Exp .  21.*  Cone  and  plate  similar  to  last;  base 
2.5  inches  in  diameter;  height  .62  inch  ;  inclination  of 
side  to  base  45°  (see  fig.  9),  .....  33.0 

“  Same  cone  without  plate,  .....  31.0 

“  Exp.  22.  Saint-Martin’s  cone  without  the  cap  ; 
to  the  upper  surface  and  around  the  opening  a  hollow 
truncated  cone  is  fitted  ;  height  .62  inch  ;  angle  of 
sides  42°  ;  larger  base  of  the  frustum  upward,  .  24.0 

“Exp.  23.  Cone  used  in  Exp.  21,  with  a  hollow 
truncated  cone,  .37  inch  high,  and  angle  of  sides  42°, 
fitted  as  in  last  experiment,  .....  24.5 

“  Exp.  24.  Cone  ;  angle  of  sides  with  base  48°  ; 
with  hollow  truncated  cone,  as  in  last  experiment,  .  25.0 

“  Exp.  25.  Cone  ;  diameter  of  lower  base  2.5 
inches  ;  diameter  of  upper  base  1.6  inches  ;  height 
.55  inch  ;  internal  diameter  at  lower  base  1.25  inches, 
and  diverging  to  1.6  inches  at  upper  base,  .  .  25.5 

“  Exp.  26.  Cone  similar  to  that  used  in  Exp.  21, 
with  a  flat  plate,  as  recommended  by  Cisalpin  (see 
fig.  6),  .7  inch  above  top  of  cone ;  diameter  equal  to 
that  of  base  of  cone  ;  on  under  surface  of  the  plate  a 
hollow  cone  .37  inch  in  height,  lesser  base  downwards,  25.0 

“  Exp.  27.  Square  block  representing  a  chimney  ; 
flue  inches  in  diameter  ;  sides  2  inches  ;  height  4 
inches  ;  one  side  towards  the  blast,  .  .  .  33.5 

“  Same,  with  corner  towards  the  blast,  .  .  .  35.5 

“  Same,  with  a  small  cone  .5  inch  high  ;  angle  of 
side  63°  ;  side  to  the  blast,  .....  37.5 

“  Exp.  28.  Same  block,  with  its  plane  upper  sur¬ 
face  inclined  towards  the  blast,  at  an  angle  of  3°  with 
the  horizon,  ........  37.0 

“  Same,  at  an  angle  of  10°  with  horizon,  .  .  39.0 

“  “  “  20°  “  “  .  .  87.0 


Velocity  per 
Second. 


Feet. 

1.61 

1.71 


2.21 


2.16 


2.12 


2.08 


2.12 

1.57 

1.49 

1.425 


1.43 

1.36 

0.609 


*  Dimensions  of  the  original  of  this  model :  —  diameter  of  flue  8  inches  ;  diam¬ 
eter  of  cone  at  base  16  inches ;  height  4  inches ;  diameter  of  plate  16  inches,  and 
4  inches  above  top  of  cone. 


OF  ARTS  AND  SCIENCES. 


(321)  17 


Time  in  Velocity  per 
Seconds.  Second. 

“  Exp.  29.  Same  block  ;  upper  surface  horizontal ; 
a  square  plate,  2  inches  by  the  side,  on  that  side  which  Feet, 

is  next  the  blast,  .......  34.0  1.56 

“  Exp.  30.  Conical  tube,  open  at  both  extremities  ; 
diameter  of  larger  opening  2  inches  ;  of  lesser  ex¬ 
tremity  1.3  inches;  length  4  inches;  inclination  of 
sides  5°  ;  centre  of  lateral  opening  1.6  inches  from 
lesser  extremity  ;  lesser  extremity  turned  towards  the 
blast,  .........  35.0  1.51 

“  Same  conical  tube ;  lesser  opening  reduced  to 
.37  inch, .  54.0  0.981 

“  Exp.  31.  Conical  tube,  open  at  both  extremities; 
diameter  of  larger  3  inches  ;  of  lesser  1.25  inches  ; 
inclination  of  sides  15°  ;  length  7  inches  ;  centre  of 
lateral  opening  1.7  inches  from  lesser  end  ;  lesser  end 


towards  the  blast,  .  .  .  .  « 

28.4 

1.87 

“  Exp.  32.  Same  conical  tube,  its  sides  continued 
until  they  form  a  cone,  with  its  apex  turned  toward 
the  blast,  ........ 

51.0 

1.039 

“  Same,  with  its  axis  making,  horizontally,  an  an¬ 
gle  of  35°  with  the  direction  of  the  blast, 

31.0 

1.71 

“  Same ;  axis  making  an  angle  of  15°  with  the  blast, 

30.0 

1.77 

tt  it  tc  <yo  tt  tt 

27.0 

1.96 

“  Exp.  33.  Conical  tube  ;  angle  of  sides  47°,  open 
at  both  extremities  ;  diameter  of  larger  extremity  4 
inches,  of  lesser  1.4  inches  ;  length  3.3  inches;  cen¬ 

tre  of  lateral  opening  from  lesser  end  1.1  inches, 

36.5 

1.45 

“  Same  tube ;  sides  prolonged,  forming  a  cone ; 
apex  towards  the  blast,  ...... 

32.5 

1.63 

Fig.  12.  Fig.  13. 

“  Exp.  34.  Conical  tube  ; 
inclination  of  sides  90°  ;  larger 
end  4  inches,  lesser  1.25  ; 
height  1.3  inches  (fig.  12),  .  28.5  1.86 

“  Same  ;  sides  prolonged, 
forming  a  cone ;  apex  to  the 
blast  (fig.  13),  .  .  .  34.0 

3 


1.56 


18  (322)  PROCEEDINGS  OF  THE  AMERICAN  ACADEMY 


“  Exp.  35.  Revolving  conical  ventilator,  accord¬ 
ing  to  the  proportions  of  the  inventor, 


Time  in  Velocity  per 
Seconds.  Second. 

Feet. 

41.0  1.29 


“  In  the  following  experiments  on  the  velocity  of  currents  through 
the  same  length  of  leaden  pipe,  the  current  was  produced  by  the  same 
blast  acting  upon  mouth-pieces  of  different  forms  and  dimensions,  ap¬ 
plied  to  the  leaden  tube  and  presented  fairly  to  the  blast. 


Fig.  14. 


“  Exp.  36.  Elbow,  opening  turned 
towards  the  blast ;  current  traversed 
leaden  pipe  in  ... 


“  Exp.  37.  Conical  tube,  Exp.  30, 
closed  at  lesser  end,  the  other  turned 
to  the  blast,  . 


19.0 


19.7 


“j Exp.  38.  Conical  tube,  Exp.  31,  closed  at  less¬ 
er  end,  the  other  turned  to  the  blast,  .  .  .  18.6 


“  Exp.  39.  Conical  tube,  Exp.  33,  closed  at  lesser 
end,  the  other  turned  towards  the  blast,  .  .  .  16.0 


“  Exp.  40.  Conical  tube,  2  inches  long ;  diame¬ 
ter  of  larger  extremity  1.25  inches;  diameter  of  less¬ 
er  .8  inch,  which  is  presented  to  the  blast,  .  .  19.7 

“  Exp.  41.  A  glass  tube,  .25  inch  bore,  and  long 
enough  to  reach  from  the  centre  of  the  trunk  beyond 
its  side,  and,  consequently,  beyond  the  influence  of 
the  blast,  was  fastened  by  one  of  its  extremities  in  a 
small  hole  bored  for  this  purpose  in  the  side  of  the 
conical  tube  used  in  the  last  experiment,  and  near  its 
larger  extremity.  The  conical  tube  was  placed  in  the 
same  position  as  before.  On  presenting  the  flame  of  a 
candle  or  any  light  substance  near  the  open  extremity 
of  the  glass  tube,  a  current  of  air  was  perceived  flow¬ 
ing  into  the  tube. 

“  Exp.  42.  Saint- Martin’s  cone  and  cap  (see  fig.  6), 
with  its  axis  parallel  with  the  blast;  blast  directly 
upon  the  top  of  the  cap,  .....  29.0 

“  Exp.  43.  Cone  of  45°,  with  flat  plate  (fig.  9), 
axis  parallel  with  the  blast,  as  in  preceding  experiment,  29.5 


2.706 

2.69 

2.85 

3.31 


2.69 


1.83 

1.80 


OF  ARTS  AND  SCIENCES. 


(323)  19 


ilocity  per 
Second. 


Feet. 

1.92 


1.08 


1.45 


1.40 


“  The  experiments  which  follow  are  on  the  influence  of  ventilators 
upon  a  current  already  established,  and  moving  with  a  certain  velocity 
in  the  same  direction  with  that  produced  by  the  ventilator.  The  cur¬ 
rent  is  established  by  placing  the  farther  end  of  the  leaden  pipe  —  that 
which  has  heretofore  been  kept  carefully  beyond  the  influence  of  the 
blast  —  in  the  blast,  in  such  a  manner  that  it  shall  receive  more  or 
less  of  its  force. 


Velocity  of  established  current  in  seconds, 
“  “  “  feet, 

29 

1.83 

15.5 

3.42 

26.5 

2.00 

Elbow  with  plate  ;  plate  towards  the  blast,  . 

lS.7 

ft. 

2.69 

II 

14  5 

ft. 

3.66 

18(.3 

ft. 

2.89 

Cone,  fig.  9,  without  its  plate, . 

26  5 

2.00 

17.2 

3.08 

.  . 

•  . 

Same,  with  its  plate, . 

26.5 

2.00 

.  , 

,  , 

.  • 

,  . 

Saint-Martin’s  cone, 

25.0 

2.12 

14.5 

3.66 

.  , 

•  • 

Saint-Martin’s  cone  and  cap, . 

26.2 

2.02 

,  . 

,  . 

26.0 

2.04 

Cone  ;  angle  of  sides  71°  ;  height  1.5  inches, 
Conical  tube,  Exp. 31,  lesser  end  to  the  blast, 

,  , 

14.2 

3.72 

.  . 

.  . 

#  # 

15.0 

3.53 

21.7 

2.46 

Conical  tube  of  47°,  lesser  end  to  the  blast, 
Conical  tube,  Exp.  30,  lesser  end  to  the  blast, 

14.5 

3.66 

16.5 

3.21 

18.2 

2.90 

Conical  cap  ;  tube  of  47°,  lesser  end  closed  and 

turned  to  the  blast, . 

Conical  tube  ;  length  2  inches ;  diameter  at 

17.0 

3.11 

smaller  end  1.25 ;  at  larger,  2  inches,  over 

which  and  1  inch  from  it  is  a  plate  2.5  inches 

in  diameter,  turned  to  the  blast ;  smaller  end 

in  the  leaden  pipe, . 

20.5 

2.58 

Elbow ;  plate  1.75  inches  in  diameter ;  .5  inch 

from  mouth  of  elbow  ;  plate  towards  the  blast, 

20.0 

2.65 

Same,  with  plate  .75  inch  from  mouth  of  elbow, 

20.75 

2.55 

Same ;  plate  2.5  inches  in  diameter,  1  inch 

from  elbow, . 

176 

3.00 

Fig.  15. 


Time  in 
Seconds. 


Fig.  16. 


“  Exp.  44.  Elbow  with  its 
mouth  towards  the  blast,  and 
covered  by  a  flat  plate,  3  inches 
in  diameter  and  1  inch  from  the 
mouth, . 27.6 

“  Exp.  45.  Same  elbow  and 
plate,  but  turned  in  the  opposite 
direction  with  reference  to  the 
blast ;  current  passed  down  the 
pipe,  and  traversed  it  in  .  .  49.0 

“Same  elbow,  with  a  curved  plate  1.75  inches  in 
diameter,  .75  inch  from  the  mouth  of  the  elbow ; 
mouth  turned  towards  the  blast,  ....  36.0 

“  Exp.  46.  Conical  tube,  4  inches  long  ;  a  plate  3 
inches  in  diameter,  and  .75  inch  distant  from  lesser 
extremity,  plate  turned  towards  the  blast,  .  .  38.0 


20  (324)  PROCEEDINGS  OF  THE  AMERICAN  ACADEMY. 

“  The  established  current  in  the  following  experiments  varied  some¬ 
what  in  the  different  experiments,  but  was  constant  during  the  same 
experiment ;  they  cannot,  therefore,  be  compared  with  each  other 
without  reference  to  the  velocity  of  the  established  current. 


Established 

Current  in 

i 

Current. 

Pipe. 

Saint-Martin’s  cone  and  cap, . 

22.7 

ft. 

2.33 

2o.5 

ft. 

2.08 

Same  cone  without  cap, . 

22.2 

2.39 

26.5 

2.00 

Cone,  fig.  9,  with  its  plate, . 

25.5 

2.08 

27.0 

1.96 

Same  cone  without  its  plate, . 

Model  of  a  chimney  ;  2  inches  by  the  side  ;  end  flat  and 

23.7 

2.27 

27.0 

1.96 

horizontal ;  4  inches  long, . 

Model  of  same  dimensions ;  top  bevelled  ;  angle  of  sides 

26.0 

2.04 

18.7 

2.83 

with  horizon  40°, . 

Same  ;  angle  of  plane  of  top  inclined  towards  the  blast, 

26.0 

2.04 

21.5 

2.47 

at  an  angle  of  15°, . 

Same ;  same  inclination ;  .75  inch  above  top  a  plate  2.5 

26.0 

2.04 

21.7 

2.44 

inch  in  diameter, . 

26.0 

2.04 

21.7 

2  44 

Same,  without  the  plate;  inclined  towards  the  blast  20°, 

26.0 

2.04 

22.6 

2  34 

Same;  inclined  towards  the  blast  30°, . 

26.0 

2.04 

29.6 

1.79 

Same,  at  same  inclination  ;  plate  .75  inch  above  the  top, 
Chimney  model,  with  flat  top  inclined  towards  the  blast, 
at  the  same  angle,  30°, . 

26-0 

2.04 

25.6 

2.07 

260 

2.04 

52.5 

1.00 

Model  and  inclination  same ;  plate  3  inches  in  diameter, 
.75  inch  above  the  top, . 

Conical  revolving  cap  ;  angle  of  sides  47°,  apex  towards 

26.0 

2.04 

42.0 

1.26 

the  blast,  . . 

24.4 

2.17 

17.8 

2.97 

Conical  cap,  fig.  12, . 

Similar  cone  with  opening  at  apex  1.25  inch  in  diameter, 

27.5 

1.92 

18.5 

2.86 

%  13, . 

18.0 

2.94 

Conical  revolving  cap  ;  angle  of  sides  47° ;  apex  to  blast, 
Same,  with  opening  at  apex,  1.25  inches  in  diameter; 

27.2 

1.94 

21.2 

2.50 

2  65 

apex  to  the  blast, . 

27.2 

1.94 

20.0 

“  The  current  established  in  the  pipe  was  raised  in  temperature 
above  that  of  the  impinging  current  or  blast,  by  placing  the  pipe  in  a 
vessel  of  hot  water.  The  current  in  the  pipe  assumed  a  temperature 
of  104°,  while  that  of  the  blast  was  64°. 

“  Elbow  with  a  plate  .87  inch  from  its  mouth  and  turned  ft.  „ 
towards  the  blast ;  temperature  of  current  64°  ;  velocity  2.08  25.5 

“  Same  ;  temperature  of  current  104°,  .  .  .  2.08  25.5 

“  Several  other  experiments  were  made,  but  the  results  coincided  so 
nearly  that  they  may  be  considered  as  identical. 

“  The  proportions  of  those  forms  of  ventilators  which  the  Commit¬ 
tee  have  found  most  efficient  will  be  placed  in  the  hands  of  manufac¬ 
turers.” 


